Plastics injection-molding machine utilizing premixed billets

ABSTRACT

The disclosure contemplates the selective supplying of a premixed plastic article of a predetermined composition into the plasticizing or melt-producing section of a plastics injectionmolding machine. Means are provided to sense the presence of a minimum amount of the article necessary to produce a predetermined quantity of melt for use in the machine and to then deliver a new premixed article into operative engagement with the plasticizing section of the machine; such delivery is so synchronized with the machine cycle as to assure that plasticizing and mold-injection phases will not be curtailed or impaired to further assure that if there is a delivery failure, the shutdown of the machine will not occur during either the plasticizing or the mold-injection phase.

United States Patent [151 9 3,698,845

Paulson p 5] Oct. 17, 1972 [54] PLASTICS INJECTION-MOLDING PrimaryExaminer-J. Spencer Overholser MACHINE UTILIZING PREMIXED AssistantExaminer-Lucius R. Frye BILLETS Attorney-Robert S. Smith, David S. Urey,Alan C.

[72] Inventor: Donald C. Paulson, Southington, Rose and Alfred LevineConn. a [57] ABSTRACT [73] Assignee: The New Britain Machine Company,

New Britain, Conn The d sclosure contemplates the selective supplying ofa premixed plastic article of a predetermined composi- [22] 1969 tioninto the plasticizing or melt-producing section of [21] Appl. No.:868,303 a plastics injection-molding machine. Means are provided tosense the presence of a minimum amount of 521 0.8. CI. ..425/145,425/166, 425/244, afticle necessary Pmduce a 00/245 quantity of melt foruse in the machine and to then 51 Int. Cl ..B29c 3/04 deliver a newPremixed article into Operative engage- 5 i l of Search 18 30 F], 30 FN,30 FQ, 30 pp ment with the plasticizing section of the machine; such 30FM, 30 FH, 3 PG, 3 CM, 3 CK, 0 delivery is so synchronized with themachine cycle as CR 30 CS 30 CV; 425/145 148 to assure that plasticizingand mold-injection phases will not be curtailed or impaired to furtherassure that [56] References Cited if there is a delivery failure, theshutdown of the machine will not occur during either the plasticizingUNITED STATES PATENTS or the mold-injection phase.

2,477,258 7/1949 MacMillin 1 8/30 FS 2,568,332 9/1951 Genovese ..l8/30Fl-l FOREIGN PATENTS OR APPLICATIONS 18 Claims, 7 Drawing Figures723,536 8/1942 Germany ..l8/30 FQ are: E co/vrem 75 ova-team? PATENTEDMI11 I912 3.698.845

INVENTOR DOA 4A0 C. PJVA fdA/ TTORNEY! PLASTICS INJECTION-MOLDINGMACHINE UTILIZING PREMIXED BILLETS The present invention relates toplastics injectionmolding machines, and in particular to a machine ofthis type to, which preformed articles having a known composition areintroduced for purposes of forming a plasticized melt.

Plastics injection-molding machines are commonly used for the productionand fabrication of articles made of plastic. In the operation of certainof these machines, a quantity of plastic material, generally in the formof plastic shavings, chips or the like, is introduced into a hopper forgravity-feed into a barrel in which an elongated plasticizing screw isrotatably positioned. The screw operates on the plastic material to forma charge of a plasticized melt which is thereafter advanced by the screwfor injection discharge through a sprue hole into a mold cavity. Uponthe completion of a molding operation, the cured product is removed fromthe mold, and the operation is repeated by the formation andintroduction of a new quantity of plasticized melt into the mold.

For many plastics molding operations, the consistency and quality of thefinished plastic product is not particularly critical, and any one of alarge variety of plastic materials may be introduced into theplasticizing section of the machine for purposesof forming the melt.However, for many molding operations, the composition, color,resiliency, hardness and/or other design criteria of the finishedproduct must be accurately controlled. For such molding operations aswell as those molding operations in which consistency of the finishedproduct is essential, it becomes necessary to utilize plastic materialhaving a known and controlled composition to form the melt. Moreover, inmany plastics molding operation, it may be desirable to periodicallyalter one or more of the characteristics of the finished molded product,such as color, so that it is necessary to periodically vary the inputplastic material in accord with the desired properties of the finishedproduct. For such molding operations, the use of plastic shavings havingan indeterminate and inconstant composition as the source of theplasticizing melt is clearly not satisfactory.

To achieve the desired control over the quality and consistency of thefinished plastic molded product, it is proposed to introduce premixedplastic articles into the plasticizing section of the machine. Thesearticles, or billets, have a predetermined plastic compositioncorresponding to the desired physical properties of the product.

In the use of such premixed billets in a machine of the characterindicated, there is a need for means for properly and reliably feedingthe billets into the plasticizing section of the molding machine, whileat the same time ensuring proper and reliable operation of theplasticizing, injection and curing phases of machine operation. Statedin other words, these phases of a machine cycle should not beinterrupted or otherwise affected by operation of billet-supplymechanism.

It is, accordingly, an object of the present invention to provide animproved plastic injection-molding machine which is particularly wellsuited for use with premixed plastic billets or the like.

It is a further object of the present invention to provide a machine ofthe type described in which a sufficient quantity of plastic materialsupplied to the machine for the purpose of forming a plasticized melt isautomatically ensured.

It is another object of the present invention to provide, in a machineof the type described, means for supplying premixed plastic billets inan automatic manner which ensures a consistently adequate amount ofmaterial for purposes of making a sufficient quantity of plasticizedmelt for molding a plastic product.

It is yet another object of the present invention to provide apparatusfor supplying premixed plastic billets into the plasticizing section ofan injection-molding machine, which can be readily adapted to operatewith existing machines of this type, and which can be varied to operatewith machines supplying varying amounts of plasticized melt.

A still further object is to meet the foregoing objects with a machinewhich requires no interruption or lengthening of the normal machinecycle.

To these ends, the present invention provides means for supplying to theplasticizing section of an injectionmolding machine, a premixed billetfrom which a plasticized melt is formed. That billet is masticated by areciprocating screw to form a predetermined quantity of plasticized meltnecessary for forming a finished product in the mold. Means are providedto sense the presence of a minimum amount of remaining billet materialin engagement with the plasticizing screw, and upon that sensing todeliver a new billet into the plasticizing section of the machine,thereby to ensure a sufficient amount of plasticizing material for eachcycle of machine operation.

The billet-feeding operation is coordinated with the machines normalplasticizing and injection cycle to allow a new billet to be deliveredonly when the plasticizing screw is de-energized and away from itsmelt-injecting position. Thus, the billet-delivery operation does notimpair or lengthen the normal plasticizing, injection and curing cycleof the machine.

Means may be provided to sense the failure of a billet delivery whenrequired, and to thereupon (except during the plasticizing, ormold-injection phase or curing phase of the machine cycle) shut down themachine. This permits either a correction of the billet-deliverymechanism or the provision of a new supply of billets, whichever isrequired.

In the embodiment herein described, the billet is urged into engagementwith the plasticizing screw by means of a plunger which is movablebetween first and second operative positions, the first position beingthe position in which it is effective to operatively cause engagementbetween the billet and the plasticizing screw. Upon the sensing of aminimum amount of billet material, and upon also sensing that themachine is in neither the plasticizing nor the injection phase of itsoperation, the plunger is caused to be raised away from the billettoward its second position, and a new billet is caused to be deliveredto the plasticizing section of the machine. The latter operation may befully accomplished during the mold-opening and mold-clamp phases of themachine cycle, so that no lengthening of the overall machine cycle needbe involved.

As herein disclosed, the means for sensing a minimum amount of remainingbillet material may comprise means for sensing the relative verticalposition of the plunger with respect to a reference point. That is, whenthe plunger has reached a minimum downward position with respect to theremaining billet material, an indication is provided that the quantityof remaining billet material is at its minimum permissible level.

The billet-delivery mechanism as herein described may comprise amagazine formed of at least one apertured plate carrying a plurality ofbillet-carrying tubes, the end of each tube communicating with one ofthe apertures formed in that plate. The magazine is incrementallyindexed or movable to positions in which successive billet tubes arecaused to register with an opening in a fixed plate; in turn, the fixedopening (or billet inlet) communicates with the plasticizing section ofthe molding machine. Each time the plunger is removed from itsbillet-engaging position upon the sensing of a minimum amount of billetmaterial, the billet-feed mechanism is indexed to cause it to move to anew position wherein a billet tube is brought into operativecommunication with the billet inlet. This, as stated above, then causesa new billet to be introduced into the molding machine.

To the accomplishment of the above and to such other objects as mayhereinafter appear, the present invention relates to a plasticsinjection-molding machine utilizing premixed billets as defined in theappended claims and as described in the following specification, takenin conjunction with the accompanying drawings, in which:

FIG. 1 is a simplified schematic diagram of a plastics injection-moldingmachine incorporating automatic plastic-billet-feed means of theinvention;

FIG. 2 is a perspective view, on an enlarged scale, of thebillet-feeding apparatus of FIG. 1;

FIG. 3 is a simplified exploded perspective view of fixed and movableparts of the billet magazine of the mechanism of FIG. 2; and

FIGS. 4 to 7 are like schematic sectional views to show a succession ofevents through which the premixed plastic article is selectivelysupplied to the plasticizing section of an injection-molding machine inaccordance with the present invention.

Briefly stated, the present invention provides an apparatus forperiodically supplying premixed plastic articles or billets into theplasticizing section of a plastics injection-molding machine. The supplyof the new billet is initiated by the sensing of a predetermined minimumamount of remaining billet material in operative engagement with theplasticizing section of the molding machine. Upon this sensing, a newbillet is positioned for operative engagement with the plasticizingsection. The billet-feed operation, when required, occurs within thenormal cycling operation of the machine, and does not interfere witheither the plasticizing or melt-injection phases of the machine.

Referring to FIG. 1 of the drawings, the invention is shown inapplication to a plastics injection-molding machine of thereciprocating-screw variety, generally designated 10, and having anelongated bed or frame 12. Frame 12 supports a mold-clamp mechanism 14at one end and plasticizing and injection mechanism at its other end.The material to be. plasticized or formed into a melt is placed inengagement with the rearward part of an elongated plasticizing screw 16which is rotated by a motor 18 having a geared connection, schematicallyindicated at 20, with screw 16. The direction of rotation of screw 16within its confining barrel 22 is such as to accomplish a plasticizingaction on the input plastic material while advancing the same toward thefront or nozzle end of barrel 22. A nozzle 24 is located at the frontend of barrel 22 and is in communicative engagement with the sprue holeor inlet port of a mold 26, secured by the clamp mechanism 14.

As is conventional in molding machines of this type, screw 16 isreciprocable on its axis and is forwardly loaded by a hydraulicallyoperated mechanism 28. The plasticized melt formed by the operation ofthe screw 16 upon the input plastic material is accumulated forward ofthe screw and forces the retraction of screw 16 until a sufficientsupply of plasticized melt has been prepared for purposes of forming -afinished plastic product in mold 26. At the time, motor 18 isde-energized, and upon the clearing of the previously molded or finishedproduct from mold 26, hydraulic mechanism 28 acts on the screw 16 tocause the front end of the screw to act as a ram to inject a new shot ofplasticized melt into mold 26. Ram pressure is maintained, with screw 16in its forward position, as long as necessary to permit the setting andcuring of the molded product in mold 26.

While the screw is still in its forward position, the plasticizingprocess is commenced for the next shot, by restarting the motor 18, andthe hydraulic pressure at 28 provides back pressure to load the retreatof the screw as the new melt is accumulated.

The control mechanism for operating the various sections of the moldingmachine 10 is conventional and is shown only schematically in FIG. 1 forpurposes of simplicity. Briefly, the cycle control 30 includes aprovision at 32 for manual start and at 34 for automatically recycledoperation. The recycle operation 34 is to be understood to includevarious safety interlocks (indicated generally at 35) which certifycertain factors of machine operation, such as proper resetting of theclamp mechanism 14 upon removal of the previously cured product frommold 26.

As described above, screw 16, upon the preparation of a suitable amountof plasticized melt, is caused to discharge a shot of the melt throughthe nozzle 24 into mold 26. At this time, hydraulic control mechanism 28receives a supply of pressure fluid from a suitable fluid control means36, as governed by a control connection 38 from the cycle control 30.When screw 16 has reached the foreward position, having just introduceda quantity of melt into mold 26, a lug 40 carried by a piston rod 42 ofhydraulic control mechanism 28 con tacts a stationary'switch 44 toinitiate in the cycle control 30 a timed dwell for maintaining a stronghydraulic feed pressure at hydraulic mechanism 28, thus assuring thatproduct-curing will proceed at a sufficient pressure level. When thedwell has been timed-out, cycle control 30 is operative through line 38to establish a substantially reduced pressure at hydraulic mechanism 28,and through line 46 to operate a motor control 48 for restarting motor18.

At this time, a new charge of melt is generated, and screw 16 is causedto return to its rearward position. The rear position may be signalledby the timed run of motor 18; however, in the form shown, lug 40contacts a second limit switch 50, connected to motor control 48 by aline 52. This causes motor 18 to be de-energized, and the clampmechanism 14 is opened to permit removal of the molded and cured productfrom mold 26.

The present invention provides means for feeding, in a controlled andautomatic manner, a supply of premixed plastic material into operativeengagement with the plasticizing section of machine 10. The inputplastic material is preferably in the form of premixed and preformedcylindrical billets which have a known, substantially unvaryingcomposition and substantially similar configuration. The billets areheld in engagement with the rotating plasticizing screw 16 which formsfrom the billet a quantity of plasticized melt. That melt subsequentlyis injected into mold 26 where the finished product is cured and thenremoved.

In the particular embodiment shown, a plurality of billets is stored ina magazine 54, which, when indexed in a manner to be described below,feeds a single billet into a billet housing 56, the lower end of whichcommunicates with the rearward end of screw 16. The billet is held inengagement with the screw by means of a plunger assembly generallyindicated as S8; in this as sembly, a plunger 60 is movable, as byhydraulic means (not shown), between a first or lower position, in whichit engages the upper end of the billet to urge it downwardly intoengagement with screw 16; and a second or retracted position, in whichplunger 60 is positioned away from the billet. When there is aninsufficient remaining amount of a billet in engagement with screw 16,from which a sufficient quantity of melt cannot be produced by screw 16for forming another finished product, plunger 60 is caused to beretracted and magazine 54 is incrementally moved to a newbillet-delivering position.

The billet-delivering operation is synchronized with the conventionaloperating cycle of the molding machine in a manner such that delivery ofa new billet, after the sensing of a minimum amount of remaining billet,is effected only when motor 16 is de-energized and is not in positionfor injecting melt into mold 26.

After a new billet is delivered into the machine from magazine 54,plunger 60 is returned to its first position to urge the remainingamount of the original billet, along with the newly-introduced billet,into engagement with screw 16 and the normal plasticizing process isthereupon re-initiated.

The means for sensing the minimum amount of billet material may comprisemeans for sensing when the lower end or head 62 of plunger 60 reaches apredetermined lowermost position. Since the volume of remaining billetis directly proportional to its vertical height, the lowermost positionof plunger 60 thus provides an accurate indication of a mini-mum amountof billet in engagement with the plasticizing screw. To this end, themotion of plunger head 62 is tracked by a lug 64 which, when head 62 isin its lowermost position (FIG. 4), contacts a position sensor such as amicroswitch 66 connected by a line 68 (FIG. 1) to a plunger controlcircuit 70.

Circuit also received an input from limit switch 50. Upon the operativecoincidence of the two input signals to circuit 70, indicating a minimumamount of remaining billet and that screw 16 is in its rearward,non-injecting position and is not rotating, a signal is produced bycircuit 70. The signal from circuit 70 is applied to a plunger control72 which, in response causes a hydraulic system (not shown) to be activethrough a hydraulic line 74 to raise plunger 60 to its second operativeposition (FIG. 5). I

As plunger 60 moves toward its second position, head 62 engages an arm78 (FIGS. 2 and 5) pivotally mounted on a pin 79 on assembly 58 as by ayoke 80. Arm 78 is mechanically linked via a flexible cable 81 to anindexing mechanism generally designated 82. The engagement of arm 78 byhead 62 causes the arm to pivot in the direction-of the arrow 83 in FIG.5, thereby to operate mechanism 82 and thus incrementally rotatemagazine 54. This in turn causes a new billet 84 (FIG. 6) to begravity-fed from magazine 54 into the upper end of a plastic billet feedor guide 85, the lower end of which communicates with-an opening 86 atthe upper end of billet housing 56. Billet 84 slides down guide 85through opening 86 and into housing 56, where it comes to rest on theremaining amount of previously supplied billet 87 (FIG. 7

At about the same time or shortly thereafter, lug 64 contacts a secondplunger-position sensor in the form of a microswitch 88 (FIG. 6)positioned vertically above the first microswitch 66, thereby to feed asignal by a line 89 to a plunger retract-certifying circuit 90. Circuit90 is connected by a line 91 to the plunger control 72 to cause, whenswitch 88 is thus actuated, the hydraulic system to be active throughhydraulic line 89 to return plunger 60 downward to its first operativeposition (FIG. 7). Plunger 60 and magazine 54 remain stationary so longas a sufficient amount of billet material remains in housing 56, afterwhen the process described above is repeated upon the next sensing of aminimum remaining amount of billet.

From the foregoing, it will be appreciated that the delivery of a newbillet into the plasticizing section of the molding machine upon thesensing of a minimum remaining amount of billet material is achievedwithout impairing, lengthening or otherwise interfering with the normaloperating cycle of the machine, and particularly the plasticizing andmelt-injection phase of that cycle.

In the event a new billet is not delivered to the plasticizing sectionof the molding machine, when required, as upon a malfunction of themagazine-indexing mechanism 82, or when the supply of billets inmagazine 54 is exhausted, it is desirable that the machine operation bestopped. However, to prevent formation of a defective product in themold, and possible damage to the machine, shutdown should preferably notoccur during either the plasticizing, mold-injection or curing phase ofmachine operation.

To this end, means are provided in the machine of this invention tocertify the delivery of a new billet and, upon the failure thereof, toprovide an appropriate indication. As herein shown, a photocell,schematically indicated at 93, is normally illuminated by a light source94. Photocell 93 and light source 94 are arranged adjacent the lower endof billet guide 85 so that the passage of a billet "F55? guide 85 intohousing 56 momentarily interrupts the light beam from photocell 93,thereby to produce an electrical signal on a line 95.

That signal is applied along with a signal from circuit 70 to abillet-feed-certifying circuit at 96. In the event that circuit 96receives a signal from circuit 70 indicating that plunger 60 isretracted, and within a predetermined time thereafter does not receive asignal from photocell 93 indicating the delivery of a new billet,circuit 96 produces a signal at its output indicating a billet-deliveryfailure.

The latter signal is applied to the input of a cycle control overridecircuit 98 which also receives input signals from switch 50 and moldinterlock 35. When the latter two signals indicate that motor 18 isde-energized and the mold is open, and when an appropriate signal is.obtained from circuit 96, circuit 98 then produces an override signalat its output, which in turn is applied to cycle control 30, thereby tocause the machine to shut down.

Magazine 54 as herein shown may comprise a pair of spaced circularplates 106 and 108. A plurality of billet-containing tubes 110 arearranged in two concentric rings between plates 106-108 and are fixedlysecured to the plates in any suitable manner to prevent movement of thetubes relative to the plates. Each of plates 106-108 is provided withapertures 109 formed in two correspondingly concentric rings 112 and114. The opposite ends of the tubes 1 are in communication withrespectively aligned pairs of apertures in plates 106-108. As seen inFIG. 3, the apertures 109 formed in the inner ring are staggered withrespect to those in the outer ring, as are tubes 110 respectivelypositioned in communication with those apertures.

Magazine 54 is mounted on a shaft 115 for incremental rotation withrespect to a fixed plate 1 16 secured to billet housing 56 by means of amounting bracket 118 (FIG. 2). A radial slot 120 is formed in plate 116and communicates with the upper end of the billet guide 85 which may besecured to plate 116 in any appropriate manner. The radial dimension ofslot 120 is sufficiently large to encompass the inner and outer rings112-114 of apertures 109 in plate 106.

When magazine 54 is caused to rotate with respect to plate 116 by meansof indexing mechanism 82, one of the apertures 109 in plate 106 and tube110 having an end in communication with that aperture are brought intocommunication with slot 120. The billet contained in that tube fallsthrough slot 120 and guide 85 into housing 56. For subsequent indexingoperations of magazine 54, different billet-containing tubes 110 arebrought into registration with slot 120 so that a billet from a tube 110in one ring will be delivered into housing 56 in one billet-feedingoperation, followed by the delivery of another billet from a tubearranged in the other ring in the succeeding billet-feeding operation.When the supply of billets in tubes 110 is exhausted, a new magazine maybe substituted, or a new supply of billets may be fed manually orautomatically into tubes 110 through the apertures in rear plate 108.

In the embodiment of the invention herein shown, indexing mechanism 82comprises an arm 122 to which one end of cable 81 is connected by aclamp 124, the other end of cable 81 being secured as described above toone end of pivotable arm 78. Arm 122 is connected to a ratchet wrench126 secured to shaft which in turn passes through a central openingformed in plate 116. The free end of arm 122 is connected to plate 1 16by means of a tension spring 128, the lower end of which is fixed to abracket 130 secured to plate 116. Spring 128 biases arm 122 in astationary position and, upon the engagement .of arm 78 by theupwardly-moving plunger 60, arm 78, acting through cable 81, causes arm122 to move against the force of spring 128 to causea single indexingoperation of ratchet mechanism 126, thereby causing the desiredincremental rotational movement of magazine 54, to bring a new billetinto registration with slot and thus into housing 56. When plunger rod60 no longer engages am 78, arm 122 is pivoted back to its normalposition by spring 128 where it remains until the arm is once againengaged and pivoted by plunger 60 during its subsequent upward movementtoward its retracted position.

The apparatus of the present invention successfully achieves its desiredresults of automatically supplying premixed plastic billets into theinjection-molding machine while at the same time ensuring that there isalways a sufficient amount of such material in engagement with theplasticizing section for the formation of an adequate supply of melt.

The delivery of a new billet (upon the sensing of a minimum remainingamount of material) is accomplished in synchronization with the normaloperating cycle of the molding machine in a manner that ensures noimpairment, lengthening or interference with either the plasticizing ormold-injection phases of that cycle. Moreover, the invention providesmeans for detecting a failure to deliver a new billet when required, andto shut down the machine at that time. Such shutdown, however, cannotoccur during either the plasticizing or mold-injection phase of machineoperation.

The billet-feeding apparatus may be provided separately of the plasticsmolding machine, in which case it may be readily adapted for use withsuch machine as by securing the billet housing 56 into communicationwith the plasticizing section of the machine, or the billet-feedingapparatus may be produced in combination with the plasticsinjectionmolding machine if desired. To increase the capacity of themolding machine, a number of billet-feeding apparatus of the typedescribed may be arranged radially about the plasticizing screw of themachine, thereby to simultaneously urge several billets into engagementwith the plasticizing screw. Moreover, to adapt the billet-feedingapparatus for different minimum remaining amounts of billet material,the relative vertical position of microswitch 66 may be adjusted.

Thus, while the present invention has been described in detail for onlya single preferred embodiment thereof, it will be appreciated thatmodifications and variations may be made therein, such as the use ofgravity-operated linear chutes instead of the reel-type magazines hereinparticularly described, and that such modifications will all be withinthe spirit and scope of the present invention as described in theappended claims.

lclaim:

1. A plastics injection-molding machine comprising plasticizing meansfor the accumulation of a plasticized melt, a cavity mold, and meanseffective to periodic ally discharge a predetermined quantity of saidmelt into said mold, means for periodically feeding to said plasticizingmeans substantially uniform plastic articles from which said melt is tobe formed, means for sensing the presence of a predetermined minimumunplasticized amount of the material of said articles in operativeengagement with said plasticizing means, and means including meansresponsive to said sensing means for introducing a succeeding one ofsaid articles into position for operative association with saidplasticizing means upon the sensing of said minimum amount, said feedingmeans comprises a plunger movable between a first operative position inwhich it operatively engages and urges one of said articles intoengagement with said plasticizing means, and a second operative positionin which it is remote from said article, said sensing means beingeffective upon the sensing of a minimum amount of said article to movesaid plunger from its said first position to its said second position.

2. The machine of claim 1, further comprising second sensing meanseffective to sense when said plunger is at its said second operativeposition, and means responsive to said second sensing means andeffective to return said plunger to its said first operative positionafterthe introduction of said second one of said articles.

3. The machine of claim 2, in which said first-mentioned sensing meanscomprises means effective to determine a relative lowermost position ofsaid plunger with respect to a reference position.

4. The machine of claim 3, in which said first-mentioned sensing meanscomprises first means arranged along the path of movement of saidplunger, and operatively engaged by said plunger when the latter is atsaid lowermost position, said second sensing means comprising secondmeans spaced above said first means in the direction of travel of saidplunger, and operatively engaged by said plunger when the latter is atits second operative position.

5. The machine of claim 4, in which said article-introducing meanscomprises feed means having one end in communication with saidplasticizing means, and means for periodically positioning one of saidarticles at the other end thereof.

6. The machine of claim 5, in which said article-introducing meanscomprises first and second apertured members, said positioning meanscomprising means for selectively causing apertures in said first andsecond members to be in substantial registration with one another andwith said other end of said feed means.

7. The machine of claim 6, in which said first member comprises a singleaperture in communication with said feed means, said second membercomprising a .plurality of apertures formed about the periphery thereof,said positioning means comprising means for selectively bringing one ofsaid plurality of apertures in said second member into registration withsaid single aperture in said first member.

8. The machine of claim 6, further comprising a plurality of open-endedcontainer means carried by said second member for holding individualones of said articles, the apertures in said second member being inrespective registration with one end of said container means.

9. The machine of claim 8, in which there are radially spaced first andsecond concentric rows of apertures in said second member, said singleaperture in said first member being radially dimensioned to overlie bothof said rows, said positioning means comprising means for selectivelyand incrementally moving apertures in one and then the other of saidfirst and second rows of apertures into registration with said singleaperture.

10. The machine of claim 9, in which said apertures in said secondmember are arranged in first and second radially spaced, staggeredconcentric rings, alternating apertures in said first and second ringsbeing in respective registration with said single aperture for eachincremental position of said article-feeding means.

11. The machine of claim 1, in which said sensing means comprises meanseffective to determine the relative position of said plunger withrespect to a reference position.

12. A plastics injection-molding machine comprising plasticizing meansfor the accumulation of a plasticized melt, a cavity mold, and meanseffective to periodically discharge a predetermined quantity of saidmelt into said mold, means for periodically feeding to said plasticizingmeans substantially uniform plastic articles from which said melt is tobe formed, means for sensing the presence of a predetermined minimumunplasticized amount of the material of said articles in operativeengagement with said plasticizing means, and means including meansresponsive to said sensing means for introducing a succeeding one ofsaid articles into position for operative association with saidplasticizing means upon the sensing of said minimum amount, saidarticle-introducing means comprises feed means having one end incommunication with said plasticizing means, and means for periodicallypositioning one of said articles at the other end thereof.

13. The machine of claim 12, in which said article-introducing meanscomprises first and second apertured members, said positioning meanscomprising means for selectively causing apertures in said first andsecond members to be in substantial registration with one another andwith said other end of said feed means.

14. The machine of claim 13, in which said first member comprises asingle aperture in communication with said feed means, said secondmember comprising a plurality of apertures formed about the peripherythereof, said positioning means comprising means for selectivelybringing one of said plurality of apertures in said second member intoregistration with said single aperture.

15. The machine of claim 14, further comprising a plurality ofopen-ended containing means carried by said second member for holdingindividual ones of said articles, the apertures in said second memberbeing in respective registration with one end of said containing means.

16. A plastics injection-molding machine comprising plasticizing meansfor the accumulation of a plasticized melt, a cavity mold, and meanseffective to periodic ally discharge a predetermined quantity of saidmelt into said mold, means for periodically feeding to said plasticizingmeans substantially uniform plastic articles from which said melt is tobe formed, means for sensing the presence of a predetermined minimumunplasticized amount of the material of said articles in operativeengagement with said plasticizing means, and means including meansresponsive to said sensing means for introducing a succeeding one ofsaid articles into position for operative association with saidplasticizing means upon the sensing of said minimum amount, saidarticle-introducing means further comprises means responsive to theoperative state of said plasticizing means, means for detecting afailure to introduce one of said articles upon the sensing of saidminimum amount, and means including means responsive to saidfailure-detecting means for terminating the operation of the machine.

17. The machine of claim 16, in which said machineterminating meansfurther comprises means responsive to the operative state of saidplasticizing means, and means responsive to the condition of said mold.

18. A plastics injection-molding machine, comprising an elongatedcylinder with an injection nozzle at the forward end, a plasticizingscrew revolvably carried in said cylinder, intermittently operablebillet-feed mechanism operative to discharge successive plastic billetsinto operative relation with a rearwardly located part of said screw,hydraulic means selectively operative to impart a forward reciprocationstroke to said screw for discharging a shot of plastics melt throughsaid nozzle, motor means operative to rotate said screw to generate afresh charge of melt forward of said screw as the accumulating meltforces retreat of said screw against back pressure from said hydraulicmeans, means sensing consumption of billet material to a predeterminedextent permitting at least one further shot injection, and synchronizingmeans responsive to said last-defined means and interlacing a cycle ofsaid billet-feed mechanism with the forward-reciprocation andmelt-generating phases of said machine, whereby injection andmelt-generation phases of the machine will be unaffected bybilletfeeding operations.

1. A plastics injection-molding machine comprising plasticizing meansfor the accumulation of a plasticized melt, a cavity mold, and meanseffective to periodically discharge a predetermined quantity of saidmelt into said mold, means for periodically feeding to said plasticizingmeans substantially uniform plastic articles from which said melt is tobe formed, means for sensing the presence of a predetermined minimumunplasticized amount of the material of said articles in operativeengagement with said plasticizing means, and means including meansresponsive to said sensing means for introducing a succeeding one ofsaid articles into position for operative association with saidplasticizing means upon the sensing of said minimum amount, said feedingmeans comprises a plunger movable between a first operative position inwhich it operatively engages and urges one of said articles intoengagement with said plasticizing means, and a second operative positionin which it is remote from said article, said sensing means beingeffective upon the sensing of a minimum amount of said article to movesaid plunger from its said first position to its said second position.2. The machine of claim 1, further comprising second sensing meanseffective to sense when said plunger is at its said second operativeposition, and means responsive to said second sensing means andeffective to return said plunger to its said first operative positionafter the introduction of said second one of said articles.
 3. Themachine of claim 2, in which said first-mentioned sensing meanscomprises means effective to determine a relative lowermost position ofsaid plunger with respect to a reference position.
 4. The machine ofclaim 3, in which said first-mentioned sensing means comprises firstmeans arranged along the path of movement of said plunger, andoperatively engaged by said plunger when the latter is at said lowermostposition, said second sensing means comprising second means spaced abovesaid first means in the direction of travel of said plunger, andoperatively engaged by said plunger when the latter is at its secondoperative position.
 5. The machine of claim 4, in which saidarticle-introducing means comprises feed means having one end incommunication with said plasticizing means, and means for periodicallypositioning one of said articles at the other end thereof.
 6. Themachine of claim 5, in which said article-introducing means comprisesfirst and second apertured members, said positioning means comprisingmeans for selectively causing apertures in said first and second membersto be in substantial registration with one another and with said otherend of said feed means.
 7. The machine of claim 6, in which said firstmember comprises a single aperture in communication with said feedmeans, said second member comprising a plurality of apertures formedabout the periphery thereof, said positioning means comprising means forselectively bringing one of said plurality of apertures in said secondmember into registration with said single aperture in said first member.8. The machine of claim 6, further comprising a plurality of open-endedcontainer means carried by said second member for holding individualones of said articles, the apertures in said second member being inrespective registration with one end of said container means.
 9. Themachine of claim 8, in which there are radially spaced first and secondconcentric rows of apertures in said second member, said single aperturein said first member being radially dimensioned to overlie both of saidrows, said positioning means comprising means for selectively andincrementally moving apertures in one and then the other of said firstand second rows of apertures into registration with said singleaperture.
 10. The machine of claim 9, in which said apertures in saidsecond member are arranged in first and second radially spaced,staggered concentric rings, alternating apertures in said first andsecond rings being in respective registration with said single aperturefor each iNcremental position of said article-feeding means.
 11. Themachine of claim 1, in which said sensing means comprises meanseffective to determine the relative position of said plunger withrespect to a reference position.
 12. A plastics injection-moldingmachine comprising plasticizing means for the accumulation of aplasticized melt, a cavity mold, and means effective to periodicallydischarge a predetermined quantity of said melt into said mold, meansfor periodically feeding to said plasticizing means substantiallyuniform plastic articles from which said melt is to be formed, means forsensing the presence of a predetermined minimum unplasticized amount ofthe material of said articles in operative engagement with saidplasticizing means, and means including means responsive to said sensingmeans for introducing a succeeding one of said articles into positionfor operative association with said plasticizing means upon the sensingof said minimum amount, said article-introducing means comprises feedmeans having one end in communication with said plasticizing means, andmeans for periodically positioning one of said articles at the other endthereof.
 13. The machine of claim 12, in which said article-introducingmeans comprises first and second apertured members, said positioningmeans comprising means for selectively causing apertures in said firstand second members to be in substantial registration with one anotherand with said other end of said feed means.
 14. The machine of claim 13,in which said first member comprises a single aperture in communicationwith said feed means, said second member comprising a plurality ofapertures formed about the periphery thereof, said positioning meanscomprising means for selectively bringing one of said plurality ofapertures in said second member into registration with said singleaperture.
 15. The machine of claim 14, further comprising a plurality ofopen-ended containing means carried by said second member for holdingindividual ones of said articles, the apertures in said second memberbeing in respective registration with one end of said containing means.16. A plastics injection-molding machine comprising plasticizing meansfor the accumulation of a plasticized melt, a cavity mold, and meanseffective to periodically discharge a predetermined quantity of saidmelt into said mold, means for periodically feeding to said plasticizingmeans substantially uniform plastic articles from which said melt is tobe formed, means for sensing the presence of a predetermined minimumunplasticized amount of the material of said articles in operativeengagement with said plasticizing means, and means including meansresponsive to said sensing means for introducing a succeeding one ofsaid articles into position for operative association with saidplasticizing means upon the sensing of said minimum amount, saidarticle-introducing means further comprises means responsive to theoperative state of said plasticizing means, means for detecting afailure to introduce one of said articles upon the sensing of saidminimum amount, and means including means responsive to saidfailure-detecting means for terminating the operation of the machine.17. The machine of claim 16, in which said machine-terminating meansfurther comprises means responsive to the operative state of saidplasticizing means, and means responsive to the condition of said mold.18. A plastics injection-molding machine, comprising an elongatedcylinder with an injection nozzle at the forward end, a plasticizingscrew revolvably carried in said cylinder, intermittently operablebillet-feed mechanism operative to discharge successive plastic billetsinto operative relation with a rearwardly located part of said screw,hydraulic means selectively operative to impart a forward reciprocationstroke to said screw for discharging a shot of plastics melt throughsaid nozzle, motor means operative to rotate said screw to generate afresh charge of melt forward of said sCrew as the accumulating meltforces retreat of said screw against back pressure from said hydraulicmeans, means sensing consumption of billet material to a predeterminedextent permitting at least one further shot injection, and synchronizingmeans responsive to said last-defined means and interlacing a cycle ofsaid billet-feed mechanism with the forward-reciprocation andmelt-generating phases of said machine, whereby injection andmelt-generation phases of the machine will be unaffected bybillet-feeding operations.